This invention concerns a power shift transmission, such as a continuously variable automatic power transmission for vehicles, which has clutches and brakes in the form of multi-disc clutches consisting of sets of discs wherein all outer discs of a disc set are supported by an outer disc carrier and all inner discs of a disc set, by an inner disc carrier, and which are engaged and disengaged by pistons.
The Applicant's DE-A 43 24 809 has disclosed a hydrodynamic multi-disc clutch for power transmission of passenger cars, trucks and work machinery having one operating cylinder, which surrounds a pressure chamber and pressure-actuated pistons placed therein for clutches consisting of disc sets, which with switching devices and transmission gears are situated around an input shaft. In this multi-disc clutch, all outer discs of a disc set are accommodated by an outer disc carrier and all inner discs by an inner disc carrier, gear clutches serving for brief interruption of the power flow, such as for the purpose of engaging a different transmission ratio.
Depending on the possible control, a difference is made here between those which can be power shifted only when parked and those which can be engaged during operation or under load. The latter are, almost without exception, so-called friction clutches in which the torque is transmitted by friction between the clutch surfaces pressed upon each other. If the friction surfaces consist of several thin discs, i.e. laminae, the clutch is designated as multi-disc clutch. Multi-disc clutches are mainly used where the gear has to be changed at high peripheral speeds. In the hydraulically actuatable clutches, oil pressure builds up in the pressure chamber surrounded by the hydraulic cylinder and the actuatable clutches placed therein.
From the Applicant's DE-A 195 06 987 has -further become known a disc synchronization for the torque-transmitting connection of two rotating parts of a power shift transmission, especially the connection of a transmission shaft with a gear wheel rotatably supported on the transmission shaft. The disc synchronization serves to simplify a manual control, since during the synchronization the speed adaptation of the transmission components to be interconnected is carried out automatically or under control. A sliding sleeve has an outer disc carrier which is connected with a switching device and an inner disc carrier, there being provided, between the disc carriers, a disc set of which adjacent discs are alternatively connected either with the inner disc carrier or with the outer disc carrier. In the case of difference of speed between the outer disc carrier and the inner disc carrier, a synchronizing torque can be obtained with the discs.
Between the synchronous body and the gearwheel is provided a clutch body in the form of clutch discs, which can mesh with an inner spline in a corresponding outer spline on the gear wheel or on the transmission shaft. The clutch bodies are axially limitedly movable, the synchronous body, on one hand, and, on the other, a spring device situated between clutch body and gearwheel forming axial limitations. With such a disc synchronization, it is possible without problem to prevent jerks and noises produced by switching with high synchronous torque and slight engagement effort at the same time.
Modern continuously variable automatic power shift transmissions have, as a rule, power shift components in the form of multi-disc brakes or multi-disc clutches. In particular for a reverse drive range, there is used here a multi-disc brake, which combined with a planetary set causes a reversal of speed and torque. The multi-disc brake is engaged mostly when parked or with low load and at low speed. In a forward drive range, the multi-disc brake will not be necessary and is idle with significant drag torque. A multi-disc brake or multi-disc clutch further needs, depending on the torque to be transmitted, requires an adequate space. The piston stroke, with the appertaining ventilation play and wear, has a negative effect.